Excel Formula Language

## Language name

The [Excel Formula Language](https://support.microsoft.com/en-us/office/overview-of-formulas-in-excel-ecfdc708-9162-49e8-b993-c311f47ca173) is likely the [most popular programming language](https://www.theregister.com/2020/12/04/microsoft_excel_lambda/) and with the introduction of LAMBDA, it's even [turing complete](https://visualstudiomagazine.com/articles/2021/01/27/excel-lambda.aspx).

Since fomulas live inside of Excel they are rarely seen as source code, however there are instances of people sharing formulas/lambdas on GitHub, so adding support for it on GitHub could be considered.

## URL of example repository

These repos are using simply the `.txt` file extension:
- https://github.com/MatrixFun/AutoXL
- https://github.com/charl-potgieter/ExcelLambdas

This repo puts the formula in the README directly:
https://github.com/UoLeevi/excel

OA Robot is using the `.lambda` file extension:
https://github.com/oehmauto/OARobot/tree/main/Getting%20Started%20Command%20Collection.xlsm%20README/Lambdas

A gist with Excel Lamda functions:
https://gist.github.com/wynhopkins/2efdf218ed78be03a0a082ff6a99dad1

## URL of syntax highlighting grammar

https://github.com/miguelangelcdm/excel-formula-formatter
(Note that the extension is advocating for the `.xlf` extension)

## Most popular extensions

`.txt` with [1.7k+ results](https://github.com/search?q=path%3A*.txt+%2F%28%3F-i%3A%3D%28LAMBDA%7CSUM%28PRODUCT%7CIF%29%3F%7CXLOOKUP%29%5C%28%29%2F&type=code)
`.xlf` with [~74 results](https://github.com/search?q=path%3A*.xlf+%2F%28%3F-i%3A%3D%28LAMBDA%7CSUM%28PRODUCT%7CIF%29%3F%7CXLOOKUP%29%5C%28%29%2F&type=code)
`.lambda` with [~100 results](https://github.com/search?q=path%3A*.lambda+%2F%28%3F-i%3A%3DLAMBDA%5C%28%29%2F&type=code)
`.excel` with [350+ results](https://github.com/search?q=path%3A*.excel&type=code)

(some search queries might need some improvement for more accurate results)

## Detected language

`None` or `XML` (when using the .xlf extension)